This study focuses on a virus recently discovered in some isolates of the protozoan parasite Leishmania. This virus was originally detected by the simultaneous presence of a unique RNA polymerase activity and a 6 kilobase RNA species in infected promastigotes. Electron microscopy revealed virus-like particles similar to picornaviruses. Viral preparations were obtained on density gradients and were found to contain the putative double-stranded RNA genome as well as RNA polymerase activity. These observations are consistent with the presence in Leishmania of a dsRNA virus. This virus is reminiscent of those found in yeast and other fungi, as well as viruses demonstrated in two other parasitic protozoan, Giardia and Trichomonas. As viral replication is dependent on the host's molecular pathways, the proposed study focuses not only on the Leishmania virus, but uses this system as a novel approach to study the transcription and translation pathways in kinetoplastid parasites. The main goals of this study are: 1)Characterize on a molecular level the replicative and translational strategy of the Leishmania virus; 2)Identify the virus-encoded proteins; 3)Establish the taxonomic status of the virus and its relationship with viruses from other protozoan and from yeast; 4)Exploit this viral system as an experimental model for studying the unique RNA processing and translation pathways in the Leishmania host.